As one of the factors of lowering the life of a rolling bearing, there is, for example, a factor that foreign matters (chips of a metal, flashes., abraded powders, etc.) are intermixed in a lubricant supplied in the bearing and these foreign matters give damages to the inner ring, the outer ring, and the rolling elements when the bearing is moved. Also, when foreign matters are intermixed in the lubricant in a bearing, it sometimes happens that the life of the bearing is shortened to about 1/10 of that of a bearing in the case that the lubricant in the bearing scarcely contains such foreign matters.
For improving lowering of the life of a bearing caused by intermixing of such foreign matters in the lubricant in the bearing, it is disclosed in JP-A-64-55423 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") that the amount of carbon of an alloy steel forming the inner ring, the outer ring, and the rolling elements and the amount of the retained austenite of the surface layer of each member are limited to the definite ranges.
On the other hand, recently, since a bearing incorporated in a transmission or an engine become a high temperature (about 130.degree. to 170.degree. C.) with the increase of the output of an engine, a bearing having a high rolling life at a high temperature has been demanded.
As a bearing having a high rolling life at such a high temperature, JP-A-3-82736 discloses the bearing wherein at least one of the inner ring, the outer ring, and the rolling elements is formed by an alloy steel prepared by adding the elements such as Si, Cr, Mo, V, etc., to a low- or middle-carbon steel and after applying thereto a carburizing treatment or a carbonitriding treatment, the member(s) are quench-hardened and tempered at a high temperature to reduce the average amount of the retained austenite below 3%.
When the inner ring, the outer ring, and/or the rolling elements are tempered at a high temperature for improving the dimensional stability at a high temperature, the hardness thereof is generally lowered but since in the bearing disclosed in foregoing JP-A-3-82736, Si, Cr, Mo, V, etc., are added to the low- or middle-carbon steel, the reduction of the hardness by such high-temperature tempering is restrained. Also, after applying a carburizing treatment or a carbonitriding treatment, quench-hardening, and tempering, the carbides of Cr, Mo, and V exist in the surface layer portion of the alloy steel, whereby the surface layer portion of the inner ring, the outer ring, and/or the rolling elements can be hardened. Thus, the abrasion resistance of each member at a high temperature is improved, whereby the rolling life of the bearing is increased.
Also, JP-A-3-153842 discloses a bearing wherein at least one of the inner ring, the outer ring, and the rolling elements is formed by an alloy steel prepared by adding the elements such as Si, Cr, Mn, (Mo), etc., to a middle-carbon steel and after applying thereto a carbonitriding treatment, each member is quench-hardened and tempered at a high temperature. By this treatment, the reduction of the hardness by high-temperature tempering is restrained and the abrasion resistance of each member at a high temperature is improved, thereby a bearing having a high rolling life is obtained.
However, in the conventional techniques described above, the technique disclosed in JP-A-64-55423 aims at the inhibition of lowering the life of the bearing by intermixing of foreign matters in the lubricant in the bearing and the techniques disclosed in JP-A-3-82736 and JP-A-3-153842 aim at the improvement of the rolling life of the bearing at a high temperature but these techniques do not consider the case of using a rolling bearing at a high temperature and in the state of containing the lubricant intermixed with foreign matters.